1. Field of the Invention
The present invention concerns a magnetic transducing element utilizing the magnetoresistance effect of a ferromagnetic tunneling junction consisting of a ferromagnet/insulator/ferromagnetic structure; it can be used in magnetic heads, magnetic sensors, magnetic memories, and other applications. In addition, the present invention concerns a magnetic head equipped with such a magnetic transducing element.
2. Background Information
In the field of magnetic recording technology, AMR (anisotropic magnetoresistive) heads utilizing the magnetoresistance effect have been employed as a read head to replace the usual inductive heads, in order to satisfy recent demands for higher recording densities; and in addition, still more sensitive spin-valve heads have been developed. Even more recently, a ferromagnetic tunneling junction magnetic transducing element has been proposed, as described in Unexamined (Laid-Open) Patent Application Publication Hei8-70149 and in the paper by Masashige Sato et al, “Magnetoresistance Effect of a Ferromagnetic Tunneling Junction with Magnetization-Fixing Layer” (Journal of the Magnetics Society of Japan, Vol. 21, No. 4-2, 1997, p. 489–492).
As shown in cross-section in FIG. 12, this magnetic transducing element has formed, on a substrate 4 (or on a base layer covering said substrate), a ferromagnetic tunneling junction film in which an insulating film 1, sufficiently thin that electrons can tunnel, is enclosed between ferromagnetic layers 2, 3, so that when electrons tunnel through the aforementioned insulating layer, a magnetoresistance effect is obtained utilizing the difference ΔR between the resistance value Rp in the state in which the magnetizations in the two ferromagnetic layers are parallel, and the resistance value Rap in the state in which they are antiparallel. Theoretically, a magnetoresistance ratio (ΔR/R) of 20 to 50%, higher than for the usual AMR elements and spin-valve elements, can be expected; and even at the experimental level, magnetoresistance ratios of approximately 10% and higher have been obtained at room temperature.
However, magnetic transducing elements based on the above-described ferromagnetic tunneling junction of the prior art are plagued by a problem in which, generally, when a bias voltage of from several tens to several hundreds of millivolts is applied, the magnetoresistance ratio is greatly decreased. For example, in the paper by Terunobu Miyazaki, “GMR of Ferromagnetic Tunneling Junctions” (Kotai Butsuri, Vol. 32, No. 4, 1997), it is reported that application of a 30 mV bias voltage causes the magnetoresistance ratio to decrease to approximately one-half its maximum value, and in the paper by A. C. Marley et al, “Voltage Dependence of the Magnetoresistance and the Tunneling Current in Magnetic Tunnel Junctions” (J. Appl. Phys. 81(8), published Apr. 15, 1997), it is reported that at 200 mV the magnetoresistance ratio decreased to approximately one-half. Such a decrease in magnetoresistance ratio accompanying application of a bias voltage is undesirable for purposes of practical application of ferromagnetic tunneling junction magnetic transducing elements.